Based upon our recent observation that polymorphonuclear leukocytes (PMNs) express receptors for the Fc portion of IgA and that this expression is enhanced on oral leukocytes from the gingival crevice, we have proposed that these receptors and the cells with which they are associated serve an important effector role in oral immune defense. The present application outlines a series of experiments which are directed toward an evaluation of the role of these receptors and cells expressing these receptors in defense on the mucosal surfaces of the oral cavity. We propose to evaluate the functional properties of oral leukocytes bearing receptors for IgA and to compare these properties with those of peripheral blood leukocytes. In addition, we would determine the role of receptors for IgA in the functional activities of these cells and the effect of various factors in modulating these functions. One approach to understanding the role in host defense of receptors for IgA and the cells with which they are associated, would involve contrasting the oral leukocytes which respond to gingivitis, both naturally occurring and experimentally induced, to those leukocytes present in the healthy gingival crevice. A second approach would use an IgA-anti-Actinomyces viscosus model system to study the ability of cells from healthy individuals and those with gingivitis to deal with this organism. Furthermore, we would investigate factors which could influence the distribution and migration of cells bearing receptors for IgA. These studies as a whole should permit a clearer definition of the role of IgA, of receptors for IgA and of the leukocyte populations bearing these receptors in oral immune defense.